JP2019127654A - Mixed powder for powder metallurgy - Google Patents

Abstract

To provide a mixed powder for powder metallurgy that can form a sintering material having excellent cutting properties.SOLUTION: An embodiment of the mixed powder for powder metallurgy according to the present invention consists mainly of an iron-based powder and contains a powder of one or more sulfides selected from among CaS, MnS, and MoSand 0.005-0.025 mass% inclusive of magnesium oxide powder, the magnesium oxide having an average particle diameter D50 of 0.5-5.0 μm inclusive. The total content of the sulfides is preferably 0.04-0.20 mass% inclusive.SELECTED DRAWING: None

Description

  The present invention relates to a powder mixture for powder metallurgy.

  In powder metallurgy, it is possible to form a sintered body having a complicated shape such as a net shape by sintering iron-based powder. Such a sintered body is used, for example, as a structural part such as an automaker part. While the demand for improvement of the dimensional accuracy of parts is increasing, it is necessary to further improve the dimensional accuracy by further cutting the sintered body.

  In addition, since there is a great demand for reducing the manufacturing cost of parts, reducing the cost of cutting is also regarded as important. In cutting, the cost can be reduced by prolonging the life of the cutting tool, but the sintered body as described above tends to be inferior in machinability and the life of the cutting tool is shortened.

  For this reason, mixed powder for powder metallurgy is used in which an iron-based powder is mixed with an additive that improves machinability and prolongs the life of the cutting tool. Specifically, for example, powders such as manganese sulfide (MnS) and sulfur (S) are used as an additive (a machinability improving material) for improving the machinability. These machinability improving materials function as a lubricant that lowers the resistance at the time of cutting, or have an action of becoming a starting point of chip division, and extend the life of the cutting tool.

  Generally, as the content of the machinability improving material in the powder mixture for powder metallurgy is larger, the machinability of the formed sintered body is improved, and the cutting tool life is extended. However, when the content of the machinability improving material is increased, mechanical properties such as radial crushing strength of the sintered material deteriorate, and dimensional change rates before and after sintering change, so a new molding die is required. There is a disadvantage in that For this reason, generally, the content of the machinability improving material in the mixed powder for powder metallurgy is about 0.3 mass% to about 0.5 mass%.

  Further, there is a large need for increasing the cutting speed due to demands for cost reduction of cutting and improvement in productivity, but the machinability improving material described above is relatively less effective in high speed cutting. When 0.3 mass% or more of sulfide is added as a machinability improving material, the sulfur evaporates during sintering to contaminate the appearance of the sintered body or contaminate the inside of the sintering furnace to damage the sintering furnace There is also a disadvantage that it becomes easier to

For example, Japanese Patent Laid-Open No. 9-279204 proposes an iron-based mixed powder for powder metallurgy containing 0.02 to 0.3 wt% of a CaO—Al ₂ O ₃ —SiO ₂ -based composite oxide powder. . In the above publication, by using a complex oxide mainly composed of Ca, the deterioration of the mechanical properties of the sintered body is reduced, the contamination of the sintered body and the sintering furnace are prevented, and the wear of the cutting tool during high-speed cutting is reduced. It is described that reduction is possible.

  However, the powder powders for powder metallurgy which are more excellent in machinability are required due to the further increase of the demand for improvement in dimensional accuracy and cost reduction of parts.

JP-A-9-279204

  In view of the said real condition, this invention makes it a subject to provide the mixed powder for powder metallurgy which can form the sintered material which is excellent in machinability.

The mixed powder for powder metallurgy according to one aspect of the present invention made to solve the above problems is mainly composed of iron-based powder, and powder of any one or more of sulfides of CaS, MnS and MoS ₂ ; And the powder of magnesium oxide is from 005% by mass to 0.025% by mass, and the average particle diameter D50 of the magnesium oxide is from 0.5 μm to 5.0 μm.

  In the mixed powder for powder metallurgy, the sulfide functions as a lubricant and forms an oxide that causes magnesium oxide particles having a relatively small particle size to adhere to the surface of the cutting tool, and the cutting tool is a sintered body It is thought that it suppresses that it is scraped off by the hard oxide in the inside. For this reason, the sintered material formed by sintering the mixed powder for powder metallurgy is excellent in machinability and can relatively prolong the life of the cutting tool.

  In the mixed powder for powder metallurgy, the total content of the sulfides is preferably 0.04% by mass or more and 0.20% by mass or less. According to this configuration, it is possible to suppress a decrease in mechanical properties and the like of a sintered material formed by sintering the mixed powder for powder metallurgy.

  Here, “iron-based powder” means pure iron powder, iron alloy powder, or a mixed powder thereof. Moreover, "mainly" means containing 90 mass% or more. The “average particle diameter D50” means a particle diameter at which the integrated volume is 50% in the particle diameter distribution measured by the laser diffraction scattering method.

  As described above, the mixed powder for powder metallurgy according to the present invention can form a sintered material having excellent machinability.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[Mixed powder for powder metallurgy]
The mixed powder for powder metallurgy according to one embodiment of the present invention is mainly composed of iron-based powder, and contains sulfide powder and magnesium oxide (MgO) powder. In addition, the mixed powder for powder metallurgy may further contain, for example, copper powder, graphite powder, powder lubricant and the like.

Iron-based powder
The iron-based powder that is the main component of the mixed powder for powder metallurgy is not particularly limited, and for example, reduced iron-based powder, atomized iron-based powder, electrolytic iron-based powder, and the like can be used.

  Further, the iron-based powder is not limited to pure iron powder, for example, steel powder obtained by pre-alloying alloying elements (pre-alloy steel powder), steel powder obtained by partially alloying alloy elements (partially alloyed steel powder), etc. These may be used in combination. The alloying elements can include, for example, copper, nickel, chromium, molybdenum, sulfur, and other known elements that improve the characteristics of the sintered body.

  The average particle diameter D50 of the iron-based powder is not particularly limited as long as it can be used as a main raw material powder for powder metallurgy, and can be, for example, 40 μm to 120 μm.

<Sulphide powder>
In a sintered body obtained by sintering the mixed powder for powder metallurgy, the sulfide remains as particles as it is. Since these sulfides are softer than the iron base that is the main body of the sintered body, they improve the machinability of the sintered body and also have lubricity to reduce the friction at the time of cutting. Increase the life span.

  Further, when the cutting speed is large, the sulfide in the sintered body is desulfurized by heat generation at the time of cutting to form an oxide. This oxide is considered to form a film that adheres to the surface of the cutting tool to protect the cutting tool, and also serves as a binder for adhering very hard magnesium oxide to the surface of the cutting tool.

As described above, any one or more of CaS, MnS and MoS ₂ can be used as the sulfide capable of efficiently improving the machinability and adhering magnesium oxide.

  As a lower limit of the total content of sulfides, 0.04% by mass is preferable, and 0.06% by mass is more preferable. On the other hand, as an upper limit of the total content of sulfides, 0.20 mass% is preferable, and 0.18 mass% is more preferable. If the total content of sulfides does not reach the above lower limit, the machinability may not be sufficiently improved. On the contrary, when the total content of sulfides exceeds the above-mentioned upper limit, there is a possibility that the mechanical characteristics of the sintered compact obtained by sintering the mixed powder for powder metallurgy may deteriorate.

  As a minimum of average particle diameter D50 of sulfides, such as CaS and MnS, 1.0 micrometer is preferred and 1.5 micrometers is more preferred. On the other hand, as an upper limit of average particle diameter D50 of sulfide, 10 micrometers is preferred and 8 micrometers is more preferred. When the average particle diameter D50 of these sulfides is less than the above lower limit, there is a possibility that it may be difficult to uniformly disperse in the mixed powder for powder metallurgy, or the mixed powder for powder metallurgy may become unnecessarily expensive. is there. On the contrary, when the average particle diameter D50 of these sulfides exceeds the above-mentioned upper limit, there is a possibility that the machinability of the sintered compact obtained by sintering the mixed powder for powder metallurgy can not fully be improved.

<Powder of magnesium oxide>
Magnesium oxide is a chemically stable hard material. For this reason, the powder of magnesium oxide is also present as fine particles in a sintered body obtained by sintering the mixed powder for powder metallurgy. The fine particles of magnesium oxide adhere to the surface of the cutting tool by the oxide generated due to the sulfide, thereby protecting the cutting tool and improving the machinability of the sintered body.

  As a minimum of content of magnesium oxide, it is 0.005 mass%, and 0.010 mass% is preferred. On the other hand, the upper limit of the content of magnesium oxide is 0.025% by mass, preferably 0.020% by mass. If the content of magnesium oxide is less than the above lower limit, the wear of the cutting tool may not be reduced. On the contrary, when the content of magnesium oxide exceeds the above upper limit, there is a possibility that the dimensional change rate at the time of sintering becomes large, and the mechanical properties such as radial crushing strength of the sintered body may be insufficient.

  As a minimum of average particle diameter D50 of magnesium oxide, it is 0.5 micrometer and 0.7 micrometer is preferred. On the other hand, the upper limit of the average particle diameter D50 of magnesium oxide is 5.0 μm, preferably 3.0 μm. When the average particle diameter D50 of magnesium oxide is less than the above lower limit, aggregation of MgO is formed. Moreover, it may not be easy to disperse | distribute uniformly in the said mixed powder for powder metallurgy. Furthermore, when the weight ratio is constant, the number of MgO particles increases, and MgO present at the boundary between the iron powder particles and the iron powder particles increases, which inhibits sintering. As a result, the dimensional change rate may increase, and mechanical properties such as radial crushing strength may be insufficient. On the other hand, when the average particle diameter D50 of magnesium oxide exceeds the above-mentioned upper limit, there is a possibility that sintering may be inhibited and strength may be reduced, the cutting tool may be chipped to accelerate wear, or magnesium oxide particles may adhere to the cutting tool The inability to do so may shorten the life of the cutting tool or may lower the processing accuracy. That is, if magnesium oxide has a sufficiently small particle size, magnesium oxide adheres to the surface of the cutting tool without increasing damage to the cutting tool so as to accelerate wear, and the life of the cutting tool can be extended.

<Copper powder>
The copper powder functions as a binder for binding iron-based powder particles to one another, and improves the strength of a sintered body obtained by sintering the mixed powder for powder metallurgy.

  As this copper powder, what is used for powder metallurgy can be used widely, for example, electrolytic copper powder, atomized copper powder, etc. can be used.

  The copper powder may be simply mixed with the iron-based powder, but may be attached to the surface of the iron-based powder using a binder, or diffused and attached to the surface of the iron-based powder by heat treatment by mixing with the iron-based powder. May be

  The lower limit of the copper powder content is preferably 0.8% by mass, and more preferably 1.0% by mass, although it depends on the strength and hardness required for the sintered body. On the other hand, as an upper limit of content of a copper powder, 5.0 mass% is preferable, 3.0 mass% is more preferable, and 2.0 mass% is especially preferable. When the content of the copper powder is less than the above lower limit, the strength improvement effect of the sintered body may be insufficient. On the contrary, when content of copper powder exceeds the above-mentioned upper limit, there is a possibility that diffusion of carbon may be inhibited and intensity of a sintered compact may become insufficient.

  As a minimum of average particle diameter D50 of copper powder, 5 micrometers is preferred and 10 micrometers is more preferred. On the other hand, as an upper limit of average particle diameter D50 of copper powder, 50 micrometers is preferred and 40 micrometers is more preferred. If the average particle size D50 of the copper powder does not satisfy the above lower limit, it may be difficult to uniformly disperse in the mixed powder for powder metallurgy, or the mixed powder for powder metallurgy may be unnecessarily expensive. . Conversely, when the average particle diameter D50 of the copper powder exceeds the above upper limit, the strength of the sintered body obtained by sintering the mixed powder for powder metallurgy may not be sufficiently improved.

Graphite powder
Graphite powder reacts with iron at the time of sintering the mixed powder for powder metallurgy to improve the strength of a sintered body obtained by forming a hard pearlite phase.

  As the graphite powder, for example, natural graphite powder, artificial graphite powder or the like can be used.

  The graphite powder may be simply mixed with the iron-based powder, but may be attached to the surface of the iron-based powder using a binder.

  As a minimum of content of graphite powder, 0.2 mass% is preferred and 0.5 mass% is more preferred. On the other hand, as a maximum of content of graphite powder, 1.5 mass% is preferred, and 1.0 mass% is more preferred. When the content of the graphite powder is less than the above lower limit, the strength improvement effect of the sintered body may be insufficient. Conversely, when the content of the graphite powder exceeds the above upper limit, the toughness of the sintered body may be insufficient.

  As a minimum of average particle diameter D50 of graphite powder, 1 micrometer is preferred and 3 micrometers is more preferred. On the other hand, as an upper limit of average particle diameter D50 of graphite powder, 30 micrometers is preferred and 20 micrometers is more preferred. If the average particle diameter D50 of the graphite powder is less than the above lower limit, it may be difficult to uniformly disperse the powder powder for the powder metallurgy, or the powder powder for the powder metallurgy may be unnecessarily expensive. . Conversely, when the average particle diameter D50 of the graphite powder exceeds the above upper limit, segregation may occur in the sintered body obtained by sintering the mixed powder for powder metallurgy and the strength may not be sufficiently improved.

<Powder lubricant>
The powder lubricant reduces friction between particles when compacting the mixed powder for powder metallurgy, improves moldability, and prolongs mold life. The powder lubricant evaporates and thermally decomposes and disappears during sintering.

  As the powder lubricant, for example, powders of metal soaps such as zinc stearate and non-metal soaps such as ethylene bisamide are used.

  As a minimum of content of a powder lubricant, 0.2 mass% is preferred and 0.5 mass% is more preferred. On the other hand, as an upper limit of content of a powder lubricant, 1.5 mass% is preferred, and 1.0 mass% is more preferred. If the content of the powder lubricant is less than the above lower limit, the powder compactability of the powder mixture for powder metallurgy may be insufficient. On the other hand, when the content of the powder lubricant exceeds the above upper limit, the density obtained by sintering the mixed powder for powder metallurgy after sintering is low, and the strength of the sintered body may be insufficient.

  As a minimum of average particle diameter D50 of a powder lubricant, 3 micrometers is preferred and 5 micrometers is more preferred. On the other hand, as an upper limit of average particle diameter D50 of a powder lubricant, 50 micrometers is preferred and 30 micrometers is more preferred. If the average particle diameter D50 of the powder lubricant is less than the above lower limit, it may be difficult to uniformly disperse in the mixed powder for powder metallurgy, or the mixed powder for powder metallurgy may be unnecessarily expensive. is there. Conversely, when the average particle diameter D50 of the powder lubricant exceeds the above upper limit, the strength of the sintered body obtained by sintering the mixed powder for powder metallurgy may not be sufficiently improved.

<Advantage>
The mixed powder for powder metallurgy forms an oxide in which sulfide functions as a lubricant and causes magnesium oxide particles having a small particle size to adhere to the surface of the cutting tool, and the cutting tool is hard in the sintered body. It is thought that it suppresses that it is scraped by an oxide etc. For this reason, the sintered material formed by sintering the mixed powder for powder metallurgy is excellent in machinability and can relatively prolong the life of the cutting tool.

[Other Embodiments]
The above embodiment does not limit the configuration of the present invention. Therefore, the above-mentioned embodiment can omit, substitute or add the components of each part of the above-mentioned embodiment based on the description of the present specification and technical common sense, and all of them are interpreted as belonging to the scope of the present invention It should.

  Hereinafter, the present invention will be described in detail based on examples, but the present invention is not to be construed as being limited based on the description of the examples.

  Mixed powder No. 1 for powder metallurgy was mixed with iron-based powder, copper powder, graphite powder, a machinability improver, magnesium oxide and powder lubricant in the proportions shown in Table 1 below. We made 1 to 15 prototypes. In addition, "-" in a table | surface shows that the material is not mix | blended.

As the iron-based powder, atomized pure iron powder "Atomel 300M" having an average particle diameter D50 of 70 μm of Kobe Steel, Ltd. was used. As the copper powder, a water atomized copper powder "CuAtW-250" having a 250 m sieve mesh of Fukuda Metal Foil & Powder Industry Co., Ltd. was used. As the graphite powder, “CPB” having an average particle diameter D50 of about 23 μm by Nippon Graphite Industries, Ltd. was used. As MnS and CaS, calcium sulfide ("CaS" in the table) having an average particle diameter D50 of 4.9 μm obtained by reducing gypsum (CaSO ₄ ) having an average particle diameter D50 of 2.4 μm in a reducing gas atmosphere such as hydrogen Alternatively, manganese sulfide ("MnS" in the table) having an average particle diameter D50 of 4.9 μm was used. As magnesium oxide, one having an average particle diameter D50 of 0.7 μm, one having an average particle diameter D50 of 2.5 μm, or one having an average particle diameter D50 of 3.2 μm was used. An ethylenebisamide wax having an average particle diameter D50 of 27 μm was used as a powder lubricant.

The above-mentioned mixed powder No. Each of 1 to 15 was compacted with a mold to form a ring-shaped compact having an outer diameter of 64 mm, an inner diameter of 24 mm, and a height of 20 mm. In the compacting, the conditions were set so that the density of the compact was 7.00 g / cm ³ . The obtained compact was sintered at a temperature of 1120 ° C. for 60 minutes in a nitrogen gas atmosphere containing 10 vol% of hydrogen gas to obtain a sintered body.

  The dimensional change ratio (molding standard and mold standard) at sintering of each trial product, radial crushing strength, and Rockwell hardness (B scale) were measured. In addition, a test was performed in which 10 sintered bodies of each trial product were stacked and the side surface was turned. As a cutting tool, a chip "SNMN 120408" using Mitsubishi Materials' cermet "NX2525" was used. As cutting conditions, peripheral speed 200 m / min, infeed amount 0.15 mm / pass, feed amount 0.08 mm / rev, dry cutting was performed, and 5287 m was cut.

  The parallel wear width (flank wear width Vb) of the flank of the cutting tool after the turning test was measured.

  The surface roughness Ra (arithmetic mean roughness) and Rz (maximum height) of the cutting surface of the sintered body after the turning test were measured. The surface roughness is measured using a surface roughness measuring instrument “SJ-410” manufactured by Mitutoyo, with cutoff values of λc = 0.8 mm, λs = 2.5 μm, and a measurement length of 5.0 mm. The average value was calculated by measuring points.

  The above measured values are summarized in Table 2 below.

  Mixed powder No. 1 for powder metallurgy containing sulfide and 0.010 mass% or more and 0.020 mass% or less of magnesium oxide. The sintered body obtained by sintering 1 to 3, 5, 7, 8, 11 and 13 has sufficient formability and mechanical strength, and the wear of the cutting tool is small.

  Furthermore, no. The sintered body prepared from 1, 5, 8, 13, 14, 15 was subjected to a test for drilling with a drill. As said drill, the coated carbide drill "AD-4D" with a diameter of 3.8 mm of OSG company was used. As processing conditions, the peripheral speed of the drill is 2 m / min (4358 rpm), the feed rate is 450 mm / min (0.103 mm / rev), and the water-soluble oil agent "Yushiroken EC50" of Yushiro Chemical Industry Co., Ltd. is sintered as a cutting oil. I cut it while putting it on my body. In order to increase the cutting distance, 180 non-through holes with a depth of 10 mm were formed.

  In the above-mentioned drilling test, the flank wear width (flank wear width Vb) of the drill was measured every time 30 non-through holes were formed. The measurement results are shown in Table 3 below.

  Mixed powder No. for powder metallurgy containing sulfide and magnesium oxide The sintered body obtained by sintering 1, 5, 8 and 13 is a mixed powder for powder metallurgy which contains no sulfide and no magnesium oxide. Compared with 14, 15, the wear of the cutting tool is small.

  Mixed powder No. 1 for powder metallurgy was mixed with iron-based powder, copper powder, graphite powder, a machinability improver, magnesium oxide and powder lubricant in the proportions shown in Table 4 below. We made 16 to 32 prototypes. In addition, "-" in a table | surface shows that the material is not mix | blended.

  Examples of the iron-based powder, copper powder, graphite powder, magnesium oxide, and powder lubricant include the above mixed powder No. 1 for powder metallurgy. The same one as 1 to 15 was used. Moreover, as a machinability improving material, the above-mentioned mixed powder No. 1 for powder metallurgy is used. The same manganese sulfide as 1 to 15 and sulfur having an average particle diameter D50 of 46.1 μm (“S” in the table) passed through a 100 mesh wire mesh and an iron sulfide having an average particle diameter D50 of 13.5 μm (“in the table FeS ") was used.

  The above-mentioned mixed powder No. 1 for powder metallurgy. 16 to 32 are mixed powder No. 1 for powder metallurgy. A ring-shaped compact is prepared by compacting with a mold in the same manner as in 1 to 15 and the resulting compact is fired at a temperature of 1130 ° C. for 60 minutes under a nitrogen gas atmosphere containing 10 vol% hydrogen gas. The sintered compact was obtained.

  The dimensional change ratio (molding standard and mold standard) at sintering of each trial product, radial crushing strength, and Rockwell hardness (B scale) were measured. In addition, a test was performed in which 10 pieces of sintered bodies of each trial product were stacked and the side surface was turned. As a cutting tool, a chip "2NU-CNGA 120408LF" using cubic boron nitride "BN 7500" manufactured by Sumitomo Electric Co., Ltd. was used. In addition, as cutting conditions, peripheral speed 200 m / min, infeed amount 0.1 mm / pass, feed amount 0.1 mm / rev, dry cutting, and 2735 m was performed.

  The parallel wear width (flank wear width Vb) of the flank of the cutting tool after the turning test was measured.

  The above measured values are summarized in Table 5 below.

  Mixed powder No. 1 for powder metallurgy containing sulfide and 0.010 mass% or more and 0.020 mass% or less of magnesium oxide. A sintered body obtained by sintering 16 to 19 and 22 to 25 has sufficient formability and mechanical strength, and the wear of the cutting tool is small.

  Copper powder, graphite powder, machinability improving material, magnesium oxide, and powder lubricant were mixed in the ratio shown in Table 6 below, and mixed powder No. 1 for powder metallurgy. Prototypes 33 to 39 were made. In addition, "-" in a table | surface shows that the material is not mix | blended.

As iron-based powder, copper powder, graphite powder, magnesium oxide and powder lubricants, the above-mentioned mixed powder No. 1 for powder metallurgy is used. The same as 1-15 was used. Moreover, as a machinability improving material, the above-mentioned mixed powder No. 1 for powder metallurgy is used. The same manganese sulfide as 1 to 15 and molybdenum disulfide having an average particle diameter D50 of 5.0 μm (“MoS ₂ ” in the table) were used.

  The above-mentioned mixed powder No. 1 for powder metallurgy. 33 to 39 are mixed powder No. In the same manner as in Nos. 16 to 32, a ring-shaped molded body was prepared by compacting with a mold, and the obtained molded body was No. It sintered on the same conditions as 16-32, and obtained the sintered compact.

  The dimensional change ratio (molding standard and mold standard) at sintering of each trial product, radial crushing strength, and Rockwell hardness (B scale) were measured. In addition, a test was performed in which 10 pieces of sintered bodies of each trial product were stacked and the side surface was turned. As a cutting tool, a chip "2NU-CNGA 120408LF" using cubic boron nitride "BN 7500" manufactured by Sumitomo Electric Co., Ltd. was used. In addition, as cutting conditions, peripheral speed 200 m / min, infeed amount 0.1 mm / pass, feed amount 0.1 mm / rev, dry cutting, and 2735 m was performed.

  The parallel wear width (flank wear width Vb) of the flank of the cutting tool after the turning test was measured.

  The above measured values are summarized in Table 7 below.

  Mixed powder No. 1 for powder metallurgy containing sulfide and 0.010 mass% or more and 0.020 mass% or less of magnesium oxide. The sintered body obtained by sintering 33 to 37 has sufficient formability and mechanical strength, and the wear of the cutting tool is small. Also, no. 33 and No. No. 34 using molybdenum disulfide as the sulfide. No. 34 used No. 4 using manganese sulfide as sulfide. The parallel wear width of the flanks is suppressed smaller than 33. Furthermore, No. 1 using two types of manganese sulfide and molybdenum disulfide as sulfides. Nos. 35 to 37 are Nos. Using only one of manganese sulfide and molybdenum disulfide as sulfides. 33 and No. The parallel wear width of the flank is suppressed smaller than 34. No. 33 and No. 18, and no. 39 and No. No. 32 has the same blending amount of various components, but it is considered that differences in measured values are caused due to differences in batches of each material.

  The mixed powder for powder metallurgy according to the present invention is suitably used to manufacture high-precision parts which need to be cut after sintering.

Claims (2)

Mainly iron-based powder,
A powder of one or more sulfides of CaS, MnS and MoS ₂ ;
And at least 0.005 mass% and at most 0.025 mass% of magnesium oxide powder,
Mixed powder for powder metallurgy, wherein the average particle diameter D50 of the magnesium oxide is 0.5 μm or more and 5.0 μm or less.   The mixed powder for powder metallurgy according to claim 1, wherein the total content of the sulfides is 0.04% by mass or more and 0.20% by mass or less.